1. Field of the Invention
The present invention relates to an ink jet recording head in an ink jet recorder, and a method for producing it. More specifically, the invention relates to an ink jet recording head with improved ejection orifices, and a method for producing a portion having the ejection orifices.
2. Description of the Prior Art
An ink jet recorder, which performs recording by ejecting a recording liquid (concretely, ink) from ejection orifices of an ink jet recording head, has been known as a recording device excellent in low noise and high speed recording. Regarding ink jet recording methods, various systems have been proposed. Some of them have been improved to reach the market, while efforts for commercialization have been made for others.
As shown in FIGS. 1 and 2, the above type of ink jet recording head comprises, for example, an ejection orifice forming member 40 having ejection orifices 41 for ejecting ink, a top plate 400 for forming ink passages 401 communicating with the corresponding ejection orifices 41, and a base plate 100 having electrothermal energy converters (hereinafter referred to as heaters) 101 each of which constitutes part of the ink passage 401 and generates energy for ink ejection. The recording head composed of these elements is constructed by integrating the top plate 400 and the base plate 100 to form a head body 4 having the ink passages 401, and joining the ejection orifice forming member 40 to the head body 4. In the drawing, the reference numeral 404 denotes an ink supply port for supplying ink to a common ink passage (not shown) in the head. The ejection orifice forming member 40 has the ejection orifices 41 of a tiny size for ejecting ink as a jet. The ejection orifice 41 is an important factor which determines the ejection performance of the ink jet recording head. Thus, the ejection orifice forming member 40 of the ink jet recording head must have properties, such as high workability for providing the tiny ejection orifices 41, and high ink resistance permitting it to withstand direct contact with ink.
Conventional materials fulfilling these requirements have been plates of metals such as SUS, Ni, Cr and Al, and films of resins which are easy to obtain, inexpensive and can be easily processed to desired thicknesses, such as polyimides, polysulfones, polyether sulfones, polyphenylene oxides, polyphenylene sulfides, and polypropylenes.
With the progress of recording technologies in recent years, there is a growing demand for high speed, high accuracy recording. Thus, the ejection orifices have been formed in a minuscule size (orifice diameter) and at a high density. Methods for forming the ejection orifice have also involved various contrivances. When the resin film is used, laser light is applied to forming ejection orifices therein, since laser light is suitable for micromachining. When the metal plate is used, ejection orifices are formed by a method such as electroforming.
However, it is extremely difficult to bond the ejection orifice forming member 40, which has the tiny ejection orifices 41 formed therein, to the head body 4 having the ink passages 401 corresponding to the ejection orifices 41. This is because it is very difficult to select an adhesive for joining the ejection orifice forming member 40 to the head body having the ink passages 401 formed therein. Depending on the type of the adhesive used, the durability of the recording head may decrease, or its operating characteristics may decline. For example, the adhesive may partly contact ink. Thus, when an adhesive with low ink resistance, such as a cyanoacrylate adhesive, is used, the adhesive undergoes attack by the ink, and is swollen and dissolved, thereby deteriorating the reliability of adhesion. As a result, peeling occurs between the ejection orifice forming member and the head body 4, decreasing the durability of the recording head.
On the other hand, assume that an adhesive with ink resistance is used. The ink resistant adhesive, especially, one of a type used as a sealing material, generally has a high cure shrinkage percentage. When this type of adhesive is cured, misalignment occurs between the ejection orifice forming member 40 and the ink passages 401 of the top plate 400, thereby deteriorating the ejection characteristics of the recording head.
As disclosed in Japanese Patent Application Laid-open No. 187342/1990, therefore, a method is employed which bonds a resin film, as a material for the ejection orifice forming member, to the head body 4, and then processes the resin film with laser light to form ejection orifices. As disclosed in Japanese Patent Application Laid-open Nos. 188257/1990 and 188258/1990, moreover, there are employed methods comprising forming an adhesive layer on the ejection orifice forming member, then forming ejection orifices in the ejection orifice forming member by stamping, and bonding the ejection orifice forming member to the head body 4.
These conventional methods, however, have been found to pose various problems to be described below, if one tries to achieve a high density head, i.e., a head with much smaller and a larger number of ejection orifices.
To increase the size and the number of the ejection orifices 41 formed in the head means to increase the accuracy of registration between the ejection orifices 41 of the ejection orifice forming member 40 and openings of the ink passages 401 of the head body 4. Also, the dimension between the adjacent ejection orifices becomes so small that an ejection orifice may be easily affected by work for forming a neighboring ejection orifice. These facts ecome main causes of the following problems:
When laser beam machining is applied after bonding of the ejection orifice forming member 40 to the head body 4, dirt, such as carbon, generated by laser ablation penetrates the ejection orifice 41, thus clogging the ejection orifice 41, or anchoring dirt onto the heater 101, thereby causing poor ejection.
When stamping is applied after formation of the adhesive layer, on the other hand, it is difficult to form the ejection orifices 41 at a higher density. This method has limits in achieving the desired high definition printing.
The ejection orifices of the ink jet recording head, desirably, is shaped such that the diameter of the ejection orifice becomes smaller the farther from the ink passage 401 and the nearer to the outside of the ejection orifice 41. Namely, the desired shape of the ejection orifice is tapered. However, the ejection orifice of a tapered form having an outwardly decreasing diameter poses the following problem: After such ejection orifices are formed in the ejection orifice forming member, an adhesive is applied thereto by a method such as transfer. The adhesive-coated ejection orifice forming member is bonded to the head body, and the adhesive is cured. As the curing adhesive shrinks, the ejection orifices and the ink passages become misaligned, causing defective ejection of ink. This misalignment is marked when the head is given a high density of ejection orifices, as stated earlier. When the ejection orifices are formed at a high density, fine misalignment of the ejection orifice at one end leads to a considerable misalignment of the ejection orifice at the other end. Eventually, misalignment becomes marked not only in a vertical or horizontal parallel direction, but also in a rotational direction, resulting in a mounting error. Thus, even with a conventional head in which the cure shrinkage of the adhesive is not problematical, the head with a high density of ejection orifices undergoes misalignment of the ejection orifices with the ink passages. It is not that the misalignment in which the ejection orifice is located within the area of the opening of the ink passage is acceptable. If the central position of the ink passage and that of the ejection orifice do not practically agree, sufficient ink ejection performance will not be obtained. Thus, a tiny amount of misalignment which has been unproblematic with a conventional head poses a problem.